Skip to main content

Full text of "Aridity indices derived from soil and climatic parameters."

See other formats


■ ^m Agriculture 



Canada 

Research Direction generate 
Branch de la recherche 

Technical Bulletin 1984-14E 




Aridity indices derived from soil 
and climatic parameters 




£ 3 0- 7 



Canada 



The map on the cover has dots representing 
Agriculture Canada research establishments. 



Aridity indices derived from soil 
and climatic parameters 



J. A. SHIELDS and W. K. SLY 
Land Resource Research Institute 
Ottawa, Ontario 



Research Branch 
Agriculture Canada 
1984 



Copies of this publication are available from: 
Land Resource Research Institute 
Research Branch, Agriculture Canada 
Ottawa, Ontario 
K1A0C6 

Produced by Research Program Service 

©Minister of Supply and Services Canada 1984 
Cat. No. A54-8/1984-14E 
ISBN 0-662- 13463-X 



TABLE OF CONTENTS 

I PERENNIAL CROPS 1 

ABSTRACT 1 

INTRODUCTION 1 

METHODOLOGY 2 

RESULTS 9 

DISCUSSION 9 

CONCLUSION 12 

ACKNOWLEDGEMENTS 12 

REFERENCES 13 

II SPRING WHEAT TO THE SOFT DOUGH STAGE 14 

ABSTRACT 14 

INTRODUCTION 14 

METHODOLOGY 14 

RESULTS AND DISCUSSION 15 

APPLICATIONS 18 

REFERENCES 18 



INDICES D'ARIDITE DERIVES DE 
PARAMETRES PEDOLOGIQUES ET CLIMATIQUES 

I. CULTURES VIVACES 

RESUME 

Nous avons mis ensemble les valeurs de capacite de retention d'eau disponible pour les vegetaux 
mesurees jusqu'a une profondeur de 120 cm et celles estimees a partir de differentes sources, 
pour des profils representatifs des sols nommes et de leurs classes texturales qui occupent de 
vastes etendues dans le sud de la Saskatchewan. L'analyse des donnees montrait que les classes 
de capacite de retention qui s'accordaient le mieux avec la base de donnees etaient celles de 100 
mm (loam sableux), 150 mm (loam), 200 mm (loam argileux) et 250 mm (argile). Nous les avons 
appelees classes reperes. Elles ont ete appliquees ensuite aux classes texturales de chaque sol 
nomme et cartographies, et nous avons trace une carte de capacite de retention d'eau disponible 
pour les vegetaux. 

Des donnees climatiques relevees dans plus de 90 stations ont servi a calculer un bilan hydrique 
quotidien pour les plantes vivaces poussant sur les sols de chaque classe de capacite de retention 
d'eau. Nous avons etabli pour la periode de releves (de 25 a 30 ans) la moyenne du deficit hyd- 
rique equivalent a l'eau d'appoint necessaire pour maintenir l'eau disponible dans differents 
sols a plus de la moitie de la capacite de retention durant toute la saison de croissance. Nous 
avons ensuite trace des cartes d'isolignes. A l'aide d'une technique de superposition, nous avons 
fait la synthese des donnees des cartes d'isolignes et de la carte de capacite de retention d'eau 
pour tracer une carte unique qui montre l'aridite generale due au climat en interaction avec 
les plantes vivaces cultivees sur des sols de differentes textures. Avec sa forme pratique, cette 
carte fournit un indice d'aridite pour les regions pedogeographiques qui passe de 100 a 450 mm 
a mesure que les besoins en eau des cultures vivaces depassent la quantite disponible. 



II. DEVELOPPEMENT DU BLE DE 
PRINTEMPS JUSQU'AU STADE PATEUX MOU 

RESUME 

Des donnees climatiques relevees dans plus de 90 stations de la Saskatchewan ont servi a cal- 
culer un bilan hydrique quotidien pour le ble en croissance jusqu'au stade pateux mou sur des 
sols de diverses capacites de retention d'eau disponible. Nous avons calcule pour la periode de 
releve de chaque station, soit en general de 25 a 30 ans, le deficit hydrique equivalent a la quan- 
tite d'eau d'appoint necessaire pour maintenir chaque sol a la moitie de sa capacite de retention 
iusqu'a ce que le ble de printemps ait atteint le stade pateux mou. Nous avons ensuite trace 
des cartes d'isolignes montrant ce deficit hydrique du au climat pour les sols ayant une capacite 
de retention d'eau de 100, 150, 200 et 250 mm. 

A l'aide d'une technique de superposition, nous avons fait la synthese des donnees des cartes 
susmentionnees et de la carte de capacite de retention d'eau disponible pour les plantes afin 
de produire une carte unique qui montre l'aridite generale due a l'effet integrateur du climat 
a long terme en interaction avec les plants de ble cultives sur differents sols. Cette carte unique 
donne des indices d'aridite allant de 50 a 350 mm dans differentes regions. 



ARIDITY INDICES DERIVED FROM 
SOIL AND CLIMATIC PARAMETERS 



I. PERENNIAL CROPS 



ABSTRACT 



Measured plant available water holding capacity 
values to a depth of 120 cm and those estimated from 
various sources were documented for profiles repre- 
sentative of named soils and their textural classes oc- 
cupying extensive areas in southern Saskatchewan. 
Data analysis showed that class groupings which 
best fit the data base were capacities of 100 mm 
(sandy loam), 150 mm (loam), 200 mm (clay loam) 
and 250 mm (clay). These were termed bench mark 
classes. They were then assigned to the textural 
classes of each named soil mapped and a plant avail- 
able water holding capacity map was compiled. 

Climatic data from over 90 stations were used to cal- 
culate a daily water balance for perennials growing 
on soils of each plant available water holding capac- 
ity class. A water deficit equivalent to the amount of 
supplemental water required to maintain plant 
available water in different soils above one-half ca- 
pacity throughout the growing season was averaged 
for the period of record (25 to 30 years) and isoline 
maps were compiled. An overlay technique was used 
combining information shown on these isoline maps 
with that shown on the plant available water holding 
capacity map to compile a single map showing over- 
all aridity due to climate interacting with perennials 
grown on different textured soils. The convenient for- 
mat of this map provides an aridity index for soil geo- 
graphic areas which increases from 100 to 450 mm as 
the perennial crop demand for water exceeds that 
which is available. 

1. INTRODUCTION 

Climatic indices for various applications have been 
derived from long term monthly data. In the Cana- 
dian System of Soil Classification (1978), soil clima- 
tic classes are grouped according to their tempera- 
ture and moisture regimes. A climatic moisture 
index was used to express the growing season precipi- 
tation as percentage of the potential water used by 
annual crops when water is readily available from a 
100 mm capacity soil. 

Plant available water holding capacity of soil (AWC) 
to the effective rooting depth is defined as the differ- 



ence between the amount of water in the soil at field 
capacity and at permanent wilting point. These phys- 
ical constants have been determined in the laborato- 
ry on disturbed soil samples and on soil cores for 
many years according to well documented procedures 
(USDA Handbook 60, 1954). In the past, these 
studies were primarily conducted as research pro- 
iects of limited scope. More recently, these analysis 
have been routinely conducted on samples taken dur- 
ing a soil survey. 

In the Prairie Provinces, a number of workers (De 
Jong 1967, Verma 1968, Shaykewich 1965, De Jong 
and Loebel 1982), have developed regression equa- 
tions relating particle size distribution to AWC. 
Their equations also include the organic carbon con- 
tent of surface horizons. 

Weather in semi-arid areas is such that much more 
water can be used by crops than is provided by natu- 
ral means. Where available, irrigation water may be 
used to supplement natural precipitation. The initial 
procedures for a weather based irrigation scheduling 
model were developed by Wilcox and Sly (1974). 
Their procedures were based on reports of daily wea- 
ther occurring on soils of varying AWC. Further 
work by Sly (1982) focussed on estimation of irriga- 
tion requirements of perennial crops for the Prairies 
Provinces; estimated irrigation requirements were 
synonymous with water deficits. A series of these 
maps showing water deficit isolines for soils of vari- 
ous AWC have been prepared and included in the Ag- 
roclimatic Atlas of Canada - Derived data (1982). 

The objective of the present study was to compile a 
map of Saskatchewan south of 53N Latitude showing 
the spatial distribution of plant available water hold- 
ing capacity classes and then to combine that map 
with climatic water deficit maps to produce a single 
map depicting the overall aridity due to climate and 
soils. Southern Saskatchewan was selected for the 
pilot study area because a data base existed for both 
long term daily climatic data and the AWC's of major 
soil types. A perennial grass crop was chosen because 
it would have national application. 



2. METHODOLOGY 



2.1 PLANT AVAILABLE WATER 
CAPACITY CLASSES OF SOILS 



The main data base for the AWC of Saskatchewan 
soils was taken from the Saskatoon map area soil sur- 
vey report (Acton and Ellis 1978) and supplemented 
with data sent to the Agrometeorology Section from 
Agriculture Canada Research Station personnel (W. 
Baier personal communication). The AWC of soil 
samples from the Saskatoon map area was derived 
from the equations of De Jong (1967) which predict 
the gravimetric water content at a matric potential 
of-1/3 and -15 atmospheres. 

Gravimetric water content for each soil texture was 
converted to volumetric water content by using bulk 
density values given by De Jong (1967). It was as- 
sumed that the water content at a matric potential of 
-1/3 atmosphere was equivalent to field capacity and 
that of -15 atmospheres was equivalent to the wilting 
point. 

The ranked AWC's of soils shown in Table 1 were con- 
sidered representative of the major soil geographical 
areas of the province. For mapping purposes, avail- 
able water capacities of 100, 150, 200 and 250 mm 
were selected as bench mark classes; these values 
represent the mediam value for each class. Sub- 
sequent work by R. De Jong (personal communica- 
tion, 1983) using measured data from over 300 Sas- 
katchewan soil profiles recorded in CanSIS sup- 
ported selection of these classes. However, it was 
noted that sandy clay loam soils had capacities closer 
to 150 mm than to 200 mm (Table 2). 

2.2 MAPPING AVAILABLE WATER 
CLASSES 



The AWC map of soils in the pilot area was prepared 
by assigning selected AWC classes (see 2.1) to map 
areas of different soil textures. The data base for soil 
area textures was taken from soil-landform maps 
prepared initially at a scale of 1:250,000 by the Sas- 
katchewan Institute of Pedology. These maps showed 
both surface and subsurface textures. Map areas 
dominated by fine sandy loam soil textures or coarser 
in the upper 120 cm were assigned an AWC of 100 
mm; very fine sandy loam and loam textures were as- 
signed 150 mm; silt loam and clay loam textures were 
assigned 200 mm, and silty clay loam through heavy 
clay textures were assigned AWC's of 250 mm. 



The above maps were then reduced photographically 
to a scale of 1:1 million and combined into one map 
showing the geographical distribution of soils with 
differing AWC. Copies of this map are available on 
request from this Institute. However, for inclusion on 
this report, the map was generalized and shown at a 
scale of 1:2 million (Figure 1). 

Areas dominated by solonetzic soils were shown by a 
separate pattern because data for AWC of these soils 
are unreliable due to the influence of their saline 
and/or alkaline subsoils (Figure 1). Although soil 
moisture is present, it may not be available to the 
plant because of its low osmotic potential, a factor not 
accounted for in the concept of available water. Dune 
sand soil areas were also assigned a special pattern 
because their AWC is significantly less than 100 mm. 
AWC was not assigned to extremely saline soils or 
those occurring on steep slopes along river valleys 
and glacial drainage channels or to organic soils. 

2.3 CLIMATIC DATA 

Although methods for processing climatic data and 
preparing water deficit maps have been published 
elsewhere (Wilcox and Sly 1974, Sly 1982), they will 
be generalized and included in the following sections. 
A complete listing of the computer programs invol- 
ved can be obtained from the Agrometeorology Sec- 
tion, Land Resource Research Institute, Research 
Branch, Agriculture Canada, Ottawa (program file 
noB253). 

Basic climatic data used in the calculations were 
daily maximum and minimum temperatures and 
daily precipitation as reported in the monthly record 
of the Atmospheric Environment Services. Daily 
temperatures were used in the calculation of poten- 
tial evapotranspiration. Data for the period 1941-70 
for 31 stations were used. These were supplemented 
by data from 61 stations with records generally rang- 
ing from 25-29 years (Table 3). 

2.4 WATER DEFICIT ESTIMATION PRO- 
CEDURES 

In using the Wilcox-Sly procedure, a daily soil water 
balance is kept throughout the growing season. 



Table 1. Ranked Available Water Capacities of some Saskatchewan Soils to a 
Depth of 120 cm 



Soil 


Taxonomic 


Soil 


AWC 


Name 


Subgroup 


Texture 


mm 


Whitesand 


Orthic Black 


Sandy loam 


56 


Chaplin 


Orthic Dark Brown 


Sandy loam 


61 


Asquith 


Orthic Dark Brown 


Fine sandy loam 


84 


Meota 


Orthic Black 


Fine sandy loam 


101 


Oxbow 


Orthic Black 


Sandy loam 


109 


Waitville 


Orthic Gray Luvisol 


Loam 


109 


Oxbow 


Rego Black 


Sandy loam 


122 


Weyburn 


Orthic Dark Brown 


Sandy loam 


135 


Bradwell 


Orthic Dark Brown 


Very fine sandy loam 


137 


Fox Valley 


Orthic Brown 


Loam 


145 


Hatton 


Orthic Brown 


Loam 


145 


Bradwell 


Eluviated Dark Brown 


Loam 


147 


Weyburn 


Orthic Dark Brown 


Loam 


147 


May fair 


Calcareous Black 


Loam 


150 


Hamlin 


Orthic Black 


Loam 


154 


Hamlin 


Eluviated Black 


Loam 


154 


Mayfair 


Orthic Black 


Sandy clay loam 


163 


Sonningdale 


Calcareous Black 


Loam 


165 


Alert 


Orthic Dark Brown 


Loam 


165 


Lorenzo 


Orthic Dark Gray 


Loam 


173 


Wood Mountain 


Orthic Brown 


Loam 


175 


Wood Mountain 


Orthic Brown 


Loam 


178 


Cypress 


Orthic Dark Brown 


Loam 


185 


Wood Mountain 


Orthic Brown 


Loam 


185 


Wood Mountain 


Orthic Brown 


Loam 


188 


Sonningdale 


Orthic Black 


Sandy clay 


190 


Kamsack 


Orthic Dark Gray 


Loam 


193 


Oxbow 


Orthic Black 


Loam 


196 


Haverhill 


Orthic Brown 


Clay loam 


198 


Blaine Lake 


Orthic Black 


Loam 


201 


Keppel 


Orthic Dark Brown 


Loam 


201 


El stow 


Orthic Dark Brown 


Loam 


201 


Bradwell 


Orthic Dark Brown 


Loam 


201 


Meeting Lake 


Orthic Gray Luvisol 


Sandy clay loam 


205 


Weyburn 


Orthic Dark Brown 


Clay loam 


208 


Krydor 


Calcareous Black 


Silty clay loam 


208 


Cypress 


Orthic Brown 


Silty loam 


208 


Weyburn 


Orthic Dark Brown 


Clay loam 


211 


Haverhill 


Orthic Brown 


Clay loam 


211 


Keppel 


Calcareous Dark Brown 


Clay loam 


213 


Hoey 


Orthic Black 


Silt loam 


213 


Elstow 


Orthic Dark Brown 


Clay loam 


216 


Blaine Lake 


Eluviated Black 


Silt loam 


216 


Craigmore 


Orthic Black 


Loam 


216 


Krydor 


Orthic Black 


Silt loam 


218 


Lorenzo 


Eluviated Dark Gray 


Sandy clay loam 


221 


Meeting Lake 


Orthic Gray Luvisol 


Silt loam 


229 



Elstow 


Orthic Dark brown 


Silty clay loam 


239 


Sceptre 


Rego Brown 


Clay 


241 


Sceptre 


Rego Brown 


Clay 


244 


Melfort 


Orthic Black 


Silty clay 


266 


Regina 


Rego Dark Brown 


Heavy clay 


272 


Sceptre 


Rego Brown 


Heavy clay 


274 


Keatly 


Rego Black 


Clay 


277 


Keatly 


Rego Black 


Clay 


277 


Keatly 


Rego Black 


Heavy clay 


279 


Sutherland 


Rego Dark Brown 


Heavy clay 


284 


Tisdale 


Rego Dark Gray 


Clay 


330 


Indian Head 


Rego Black 


Heavy clay 


333 



Table 2. Measured available water capacities of textures from Saskatchewan 
soil profiles entered in CanSIS 1 . 



Texture 


AWC 


No. of 
Profiles 


Medium Sand 


21 


11 


Fine Sand 


18 


6 


Loamy fine sand 


35 


1 


Sandy loam 


134 


10 


Coarse sandy loam 


117 


20 


Fine sandy loam 


108 


12 


Very fine sandy loam 


133 


6 


Loam 


175 


98 


Silt loam 


219 


14 


Sandy clay loam 


133 


9 


Clay loam 


202 


76 


Silty clay loam 


238 


25 


Clay 


227 


19 


Silty clay 


229 


16 


Heavy clay 


268 


16 



1 R. De Jong personal communication, 1983 



Table 3. Climatological Stations in study Area. 



Alsask 


Kipling 


Pennant 


Aneroid 


Kindersley 


Pilger 


Arran 


Klintonell 


Porcupine Plains 


Bangor 


Kuroki 


Prince 


Beechy 


Kwioki 


Prince Albert 


Biggar 


Leader 


Raymore 


Broadview 


Leross 


Redvers 


Cameo 


Leader 


Regina 


Canora 


Leross 


Roadene 


Cardross 


Limerick 


Rosetown 


Carlyle 


Lloydminister 


Saskatoon, Airport 


Car on 


Loon Lake 


Saskatoon, C.D.A. 


Ceylon 


Lost River 


Scott 


Chaplin 


Lumsden 


Shaunavon 


Choiceland 


Macklin 


Spiritwood 


Consul 


Maple Creek 


St. Walburg 


Dafoe 


Mankota 


Strasbourg 


Davidson 


Meadow Lake 


Swift Current, C.D.A. 


Dundurn 


Melfort 


Swift Current, Airport 


East Poplar 


Melville 


Tisdale 


Estevan 


Merry Flat 


Tugaske 


Francis 


Midale 


Val Marie 


Glaslyn 


Moosomin 


Waseca 


Gravelbourg 


Moose Jaw 


Waskesiu 


Gull Lake 


Muenster 


Watrous 


Hafford 


Nipawin 


West Poplar 


Hudson Bay 


North Battleford 


Wilcox 


Hughton 


Outlook 


Willow Creek 


Indian Head 


Ormiston 


Wynyard 


Inglebright Lake 


Oxbow 


Yellowgrass 


Kamsack 


Pelly 


Yorkton Airport 


Kelliher 








V1U381V 



When the growing season begins, soil water is de- 
pleted at the rate of potential evapotranspiration and 
increased by rainfall. When the added rainfall re- 
sults in a figure greater than capacity, the excess is 
considered lost to runoff or percolation. 

The procedure is designed so that sufficient water is 
always available to keep tbe crop transpiring at its 
potential rate. It is generally believed that for most 
crops, the minimum water content non-limiting to 
growth is about 50% of the AWC of the soil (Pair et 
al. 1969). When plant available water is reduced to 
50% of capacity, water is added to bring the soil back 
up to its full capacity. The total of these supplements 
constitutes the water deficit for the growing season. 
These are then averaged over the number of seasons 
that climatological data are used in the calculations. 

The basic assumptions include the following: 

— The crop was a perennial grass crop with a rooting 
zone of 120 cm and which covered the soil during the 
growing season. 

— At the start of the growing season in the year pre- 
vious to the period under study, soil moisture reserve 
was assumed to be 3/4 of AWC . 

— The growing season began on the day the 5-day 
running mean air temperature reached and stayed 
above 5 .5C and ended the day it dropped below 5.5C . 

— Rain entered the soil until field capacity was 
reached. Any excess was considered lost to runoff or 
deep percolation. 

— Evapotranspiration continued at the potential 
rate during the growing season as long as plant avail- 
able water in the soil is at least one-half the possible 
maximum for the soil. Thereby, the consumptive use 
factor was always one. 

— To estimate soil water at the start of each growing 
season, soil water and the contribution to it made by 
snow or rain during the dormant season was esti- 
mated using the over-winter procedures of the versa- 
tile soil moisture budget developed by Baier et al. 
(1972, 1979). This procedure permitted the program 
to run continuously during the entire data period. 

— Supplemental water was added only when AWC of 
the soil was reduced to 50% of maximum. 



— Each water supplement was equal to 1/2 AWC and 
was applied in one day. When a supplement was re- 
quired near the end of the growing season, only 
enough water was added to maintain the soil at 1/2 
AWC until the end of the growing season. 

2.5 MAPPING ARIDITY INDEX CLASSES 

2.5.1 Water deficit maps were prepared by spacial 
interpretation of point information. The first ap- 
proach to use point data as input to the SYMAP com- 
puter program was described by Williams and Sharp 
(1972). The output provided an objectively obtained 
visual distribution of water deficits but disregarded 
the effects of physiography and well established soil 
patterns. These interpolations were then subjec- 
tively adjusted to take into account, in a general way, 
the physiography and zonal soil patterns. Distribu- 
tion of other related elements such as rainfall and 
seasonal water deficits which have been determined 
from more dense grid square data patterns were also 
considered(R. Stewart personal communication). 
The map showing climatic data deficit isolines for a 
perennial crop grown on soils with 150 mm AWC is 
presented in Figure 2. Water deficit maps for soils 
with AWC of 100, 200 and 250 mm are similar to 
those compiled by Sly (1982). These water deficit 
maps were adjusted photomechanically to a scale of 
1:1 million and produced on matte surface film. 

2.5.2 Matte surface film was overlain and affixed to 
the map showing AWC of soils prepared at a scale of 
1:1 million (see section 2.2). 

2.5.3 The AWC map of soil geographic areas (with 
attached matte film) was then superimposed on the 
climatic water deficit isoline map for 150 mm capac- 
ity soil (Figure 2). After registration of the two maps, 
attention was focussed only on AWC map areas of 
150 mm. When such an area occurred within the 
boundary conditions of a particular isoline, it was im- 
mediately traced on the upper matte overlay and as- 
signed the isoline value. In cases where an isoline or 
isolines transected such an area, the area was sub- 
divided according to the isoline pattern, then traced 
on the matte overlay and each sub area assigned the 

appropriate isoline value. This procedure was con- 
tinued until all soil areas with 150 mm AWC were as- 
signed appropriate isoline values and the boundary 
conditions for these values traced on the upper matte 
overlay. 







a 

IS 

i 



(N 

E 



2.5.4 The previous step (2.5.3) was repeated by 
superimposing the AWC map on the climatic water 
deficit isoline map for 100 mm capacity soils. Simi- 
larly, the AWC map was superimposed on the isoline 
maps for 200 and 250 mm capacity soils. 

2.5.5 The mapping procedure was completed by 
eliminating small, fragmented areas and by making 
minor line segment adjustments to align with major 
physiographic or soil zone boundaries. 

3. RESULTS 

In this bulletin, water deficit resulting from long 
term climate interacting with perennial crops grown 
on soil areas of differing AWC has been used to indi- 
cate (or index) the overall aridity of a geographical 
area. Thereby, this interaction provided a convenient 
aridity index (AI) that increased as the perennial 
crop demand for water exceeded that available in a 
given soil. 

In the south part of Saskatchewan, the AI ranged 
from over 450 mm in the extreme southwestern part 
of the agricultural region to less than 100 mm in the 
extreme northeastern part (Figure 3). The general 
pattern of AI resembles that of the major soil zones, 
particularly, the Dark Brown - Black separation. The 
resemblance to the most arid agroclimatic subregion, 
3Cm, was also strongly apparent in the southwest 
part of the province (Shields et al. 1968). 

Of particular interest is the transect A-B extending 
over a large soil area characterized by an AWC of 150 
mm. In this case, the increase in AI from 100 mm in 
the north-east (B) to 400 mm in the south-west (A) re- 
flects solely the increase in atmospheric water deficit 
resulting from lower precipitation and higher poten- 
tial evapotranspiration. 

Another area of interest is the long north-south 
transect C-D along 108W longitude. Proceeding 
northward from the U.S. border, the increase in pre- 
cipitation coupled with lower potential evapotranspi- 
ration results in decreasing atmospheric water defi- 
cits as shown in Figure 2. Assuming similar soil prop- 
erties, this would also give rise to a corresponding de- 
crease in AI. However, northward from the USA bor- 
der there is also a progressive decrease in the AWC 
of soil from 250 to 100 mm which compensates for the 
declining atmospheric water deficit. These compen- 
sating factors result in an AI of 300 to 400 mm which 
extend nearly continously from the semi-arid south- 



ern Brown soils to subhumid Black soils along the 
northern edge of the area mapped. 

The possibility of applying aridity ratings to other 
climates was also tested. Aridity indices were esti- 
mated for perennials growing on soils of varying 
AWC under climates prevailing at 6 stations in On- 
tario and 3 stations west of Saskatchewan * Table 4). 
Indices ranged from 600 mm for sandy soils at Kam- 
loops to only 71 mm on clay soils at Belleville, On- 
tario. 

As shown in Table 4, increasing AWC of soils gives 
rise to decreasing AI at localities both in the east and 
west. Although the magnitude of the AI is much 
greater at the western stations, their range across 
available water capacities is considerably less than 
for those in the east. In the east, fine textured soils 
with capacities of 200-250 mm are able to take ad- 
vantage of the relatively heavy growing season rain- 
fall. In the west, daily rainfall is frequently not even 
sufficient to fill the coarser soils to capacity. Under 
these conditions, if both fine and coarser textured 
soils are dry, the daily contribution to AI will be ap- 
proximately the same. 

A cursory review of the range in AI shown in Figure 
3 and Table 4 indicated that a sensible number of 
classes must be established. From the existing data, 
the following class limits were selected: 100, 150, 
200, 250, 300, 350, 400, 450 and 50, and 550 mm. 

4. DISCUSSION 

Areas shown on the AWC maps reflect texture of sur- 
face soils and parent materials shown on soil-land- 
form maps prepared by the Saskatchewan Institute 
of Pedology; these maps were interpreted and 
generalized from more detailed soil survey maps. 

Although the existing data base for the AWC of Sas- 
katchewan soils is not comprehensive, it does include 
the dominant soil associations and textures mapped 

in the study area. As indicated previously (see 2.2), 
very fine sandy loam and loam textures were as- 
signed an AWC of 150 mm. These textures are char- 
acteristic of the Bradwell and Weyburn soil associa- 
tions in the Dark Brown soil zone or their equivalents 
in the Brown or Black soil zones. In general, lacus- 
trine or eolian soils characterized by silt loam tex- 
tures had an AWC of 200 mm reflecting the contribu- 
tion of higher silt contents to AWC. Organic matter 



10 



CD 




w 




v> <S 

8 8s 
file. 

= o 
Q z 



S 



Q 

Z 
LU 

a 




-o 

C 
o 
c 
9 

o 



T3 

a 



'C 
< 



11 



Table 4. Aridity Indices Estimated at Selected Climatological 
Stations in Canada, 1941-70, Perennials 



Station 



Kamloops 
Summer] and 
Medicine Hat 

Average 



100 

612 
493 

478 

499 





AWC (mm) 




150 


200 


250 


577 


559 


539 


460 


434 


414 


429 


401 


386 



462 



436 



415 



Belleville 


178 


137 


97 


71 


Guelph 


193 


147 


114 


89 


Vineland 


185 


147 


109 


79 


Delhi 


221 


185 


147 


114 


Woodslee 1 


241 


191 


163 


127 


Harrow 


244 


191 


160 


130 



Average 210 

1 Woodslee data is for 1947-75 



166 



132 



102 



content is also known to influence AWC. Con- 
sequently, additional data are required to establish 
whether the loam soils of the Thick Black soil zone 
are also characterized by 200 mm capacities; pre- 
sently they were assigned a 150 mm capacity. As 
more data become available and accessible, the map 
will be updated. 

The display on one map, of aridity indices reflecting 
the combined droughtiness due to climatic and soil 
attributes for a given crop is unique. The aridity 
index of a geographical area represents the long term 
average supplemental water required to maintain 
plant available water content of a soil under peren- 
nials at a level greater than or equal to one-half of ca- 
pacity throughout the growing season. This index 
thereby provides an important link between the ef- 
fects of long term climatic data interacting with 
given soil and crop characteristics. The larger the 
aridity index, the drier the area in terms of the abil- 
ity of nature to supply the required amount of grow- 
ing season water to perennials growing on a particu- 
lar soil. 

As discussed earlier, the climatic moisture defini- 
tion, at the Soil Family Taxonomic level assumes a 
single soil AWC of 100 mm thereby oversimplifying 
a complex system. In contrast, climatic parameters 
interacting over a range of AWC's provide the capa- 
bility to derive aridity indices representative of soil 



geographical areas characterized by known soil pa- 
rameters. The outlined procedures thereby provide 
the flexibility to integrate various climatic and soil 
parameters in a practical mode for display as a single 
map depicting overall aridity for perennial crops. 

The assumptions under which the estimations used 
in this study (see methodology) indicate that water 
deficits mapped are probably the average likely to 
occur. Although it is generally believed for most 
crops that the minimum non-limiting water content 
within the rooting zone is 50% AWC (Pair et al., 
1969), most crops can produce an adequate yield 
when available water drops to less than 50% of AWC. 
The techniques employed in making these estima- 
tions are such that they can be adjusted to take into 
account these various crop characteristics. 

4.1 APPLICATION OF ARIDITY INDICES 
TO THE SOIL WATER INVESTIGATION 
GROUP (SWIG) 

The soil water regime classification for describing 
Canadian soils is currently under revision (Nowland, 
1979). The revised framework encompasses classes 
for soil transmissability, saturation zones and wet- 
ness persistence. Water deficit classes taken from 
Soil Family Criteria are also included as are water 
retention classes. Discussion of the revised 
framework is confined to evaluating proposed soil 
water deficit and water retention classes. 



12 



Prior discussion has indicated that Climatic Mois- 
ture Indices (CMI) definitive of soil families assumed 
a single AWC of 100 mm characteristic of a sandy 
loam. The formula for calculating CMI is such that 
the value used for AWC has a relatively small effect 
on the resulting value of the index (Sly, 1970), par- 
ticularly in arid regions. Consequently, the CMI can- 
not be considered as adequately representing differ- 
ences in soils of varying A WC's. The procedures de- 
scribed herein overcome this limitation providing a 
valuable improvement. In spite of the obvious advan- 
tage of the new approach, there are some factors 
which must be considered. These factors relate 
primarily to the data base requirements as follows: 

— Long term daily temperature and precipitation pa- 
rameters are required for calculating the soil water 
balance. This data base must be reviewed on an na- 
tional perspective. For example, Saskatchewan and 
Manitoba have a satisfactory number of long term 
climatic stations but southern Alberta does not. The 
data base for central Atlantic Canada is under cur- 
rent review. 

— AWC of major soils — Sufficient data exists in the 
Prairie Region to prepare maps showing the AWC of 
soil geographical areas. The data base for Ontario, 
Quebec and Atlantic Canada must also be reviewed. 

— At best, the data base can be used to derive an AI 
for relatively large soil geographical areas. The 
index is representative of midslope positions within 
a given soil landscape. At present it cannot be ad- 
justed to different slope position (summit, midslope, 



footslope) influencing runoff and consequently water 
storage; cover type is also a factor. Only a very lim- 
ited amount of slope specific data was reported by 
Ayres (1972, personal communication) in the Swift 
Current map area. His results indicated that mois- 
ture contents in midslope position was less than of 
that in footslope position but considerably more than 
that at the summit position. 

Despite the cimatic data base limitations coupled 
with the lack of slope specific AI capabilities, the au- 
thors believed that AI estimates constitute an impor- 
tant component of the Soil Water Regime Classifica- 
tion. When this proposed classification is considered 
in its entirety, the data base for estimating AI may 
well be as complete as the data base currely used for 
estimating other components such as saturation 
zones and persistence classes. 



5. CONCLUSION 

Integration of climatic and soil parameters interact- 
ing with perennial crop growth into a single map pro- 
vided a convenient format for displaying the overall 
aridity distribution within the study area. 
Methodologies used for compilation of this map 
should now be extended over the entire Prairie ag- 
ricultural region to provide local comparisons of the 
aridity index which increases as the plant demand 
for water exceeds that available in a given soil. 
The procedures should also be modified for mapping 
aridity indices for cereal crops such as wheat. 



ACKNOWLEDGEMENTS 

The authors wish to thank the Saskatchewan Institute of Pedology for permission to use data 
from the CanSIS files. 



13 



REFERENCES 

Acton, D.F. and Ellis, J.G. 1978. The Soils of the Saskatoon map area, 73-B, Saskatchewan. Sask. Institute of Pedology 
Publication, S4, Extension Division University of Saskatchewan, Saskatoon. 

Agriculture Canada. 1976. Agroclimatic Atlas of Canada - Derived Data. Agrometeorology Research and Service, 
Chemistry and Biology Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario. K1A 0C6 19 pp. 

Baier, W., Chaput, D.Z., Russelo, D.A., Sharp, W.R. 1972. Soil moisture estimator program system. Tech. Bull. 78. 
Agrometeorol. Sect. Res. Branch, Agr. can. 55 p. 

Baier, W., Dyer, J. A., and Sharp, W.R. 1979. The versatile soil moisture budget, Tech. Bull. 87. Agrometeorol. Sect. 
Res. Branch, Agr. Can. 51 p. 

Canada Soil Survey Committee. 1978. The Canadian System of Soil Classification. Can. Dep. Agr. Publ. 1646. Supply 
and Services Canada, Ottawa. 

De Jong, E. 1967. Moisture retention of selected Saskatchewan soils In Soil Plant Nutrient Research Report. Sas- 
katchewan Institute of Pedology Report No. M6. Univ. of Saskatchewan, Saskatoon. 

De Jong, R. and K. Loebel. 1982. Empirical relations between soil components and water retention at 1/3 and 15 atmos- 
pheres. Can. J. Soil Sci. 62: 343-350. 

Nowland, J.L. 1979. Progress Report - Soil Water Working Group. In Proceedings of Expert Committee on Soil Survey, 
Ottawa March 20-23, 1979. Research Branch, Agric. Canada. 

Pair, C.H., Hinz, W.W., Reid, W. and Frost, K.R. 1969. Sprinkler Irrigation. Sprinkler Irrigation Assn., Washington, 
D.C.444p. 

Shakyewich, C.F. and Zwarich, M.A. 1965. Relationships between soil physical constants and soil physical compo- 
nents of some Manitoba soils. Can. J. Soil Sci. Vol. 48, 199-204. 

Shields, J. A., Rostad, H.W.P., and Clayton, J.S. 1968. A Guide to soil capability and land inventory maps in Saskatche- 
wan. Publication M8. Sask. Institute of Pedology, Univ. of Saskatchewan, Saskatoon. 

Sly, W.K. 1970. A climatic moisture index for land and soil classification in Canada. Can. J. Soil Sci. 50: 291-301. 

Sly, W.K. 1982. Agroclimatic Maps for Canada - Derived Data, Soil water and thermal limitations for spring wheat 
and barley in selected regions. Tech. Bull. 88, Agrometeorology Section, Land Resource Research Institute, Research 
Branch, Agr. Canada, Ottawa. Kl A 0C6. 

United States Dept. of Agric. Handbook No. 60. 1954. Diagnosis and improvements of saline and alkaline soils. United 
States Salinity Laboratory Staff. 

Verma, I.R. 1968. Moisture balance in soils of the Edmonton area. Ph.D. Thesis Dept. Soil Sci. Univ. of Alberta. 204 
P 

Wilcox, J.C. and W.K. Sly. 1974. A weather based irrigation scheduling procedure. Tech. Bull. 83 Agrometeorol. Sect. 
Res. Branch, Agr. Can. 23 p. 

Williams. G.D. V. and Sharp, W.R. 1972. Computer mapping in agrometeorology Tech. Bull. 80. Agrometeorology Sec- 
tion, Land Resource Research Institute, Research Branch, Agr. Canada. 40 pp. 



14 



ARIDITY INDICES DERIVED FROM 
SOIL AND CLIMATIC PARAMETERS 

II. SPRING WHEAT TO SOFT DOUGH STAGE 



ABSTRACT 



Climatic data from over 90 stations in Saskatchewan 
were used to calculate a daily water balance for grow- 
ing wheat to the soft dough stage on soils of varying 
plant available water holding capacity. The water 
deficit equivalent to the supplemental water re- 
quired to maintain each soil at one-half capacity to 
the soft dough stage was averaged over the period of 
record for each station, generally from 25-30 years. 
Isoline maps were then prepared showing this clima- 
tic water deficit for soils with water holding 
capacities of 100, 150, 200 and 250 mm. 

An overlay technique combining the above maps 
with a plant available water holding capacity map 
was used to compile a single map showing overall 
aridity due to the integrating effect of long term cli- 
mate interacting with wheat plants grown on differ- 
ent soils. This single map displays aridity indices 
ranging from 50 to 350 mm in different areas. 

1. INTRODUCTION 

Prairie weather conditions are such that insufficient 
water is provided by natural means to attain poten- 
tial yields of spring wheat. This water deficiency is 
due to the combination of inadequate spring soil 
moisture reserves and growing season precipitation. 
Soil moisture reserves which are available to the crop 
are dependent on soil texture and organic matter con- 
tent (De Jong 1967, De Jong and Loebel 1982, Verma 
1969). Variability in local droughtiness is therefore 
a function of stored water available to plants, grow- 
ing season precipitation and evapotranspiration. 
Knowledge of long term climatic water deficit pat- 
terns interacting with plant available water holding 
capacity patterns can thereby be integrated to pro- 
vide an indication of aridity of soil geographic areas 
for growing wheat. 

Procedures using climatic and soil parameters have 
recently been developed to compile a single map 
showing the aridity index (AI) of different soil geo- 
graphic areas for growing perennial crops as reported 
in Section I. This single map provided a convenient 
format for displaying the combined aridity due to cli- 
mate and soils; the aridity index increased as the de- 



mand for water by perennials exceeded that avail- 
able in a given area. 

The objective of this study is to prepare a map of 
southern Saskatchewan showing the overall aridity 
due to climate and soils for wheat grown to the soft 
dough stage. The date of the soft dough stage was 
selected for demonstration purposes because it is 
near the end of the growing season and provides rela- 
tively large index values. These indices when shown 
on a single map provide a useful and convenient com- 
parison of aridity in different soil geographic areas. 

2. METHODOLOGY 

2.1 PLANT AVAILABLE WATER HOLD- 
ING CAPACITY CLASSES AND MAP 
COMPILATION 

The basic data base for plant available water holding 
capacity (AWC) of Saskatchewan soils was similar to 
that reported previously in Section I. This data was 
complemented by estimates derived from equations 
of De Jong and Loebel (1982) applied to all Sas- 
katchewan soil profiles entered in CanSIS for which 
the necessary data were complete. Their equations 
predicted the gravimetric water content at a matric 
potential of -1/3 and -15 atmospheres which were as- 
sumed equivalent to field capacity and wilting point, 
respectively. Gravimetric water content for each soil 
texture was converted to volumetric water content by 
using bulk density values from equations developed 
by R. De Jong (personal communication). 

Benchmark plant available water holding capacity 
classes of 100 mm for sandy loam, 150 mm for loam 
and very fine sandy loam, 200 mm for silt loam and 
clay loam and 250 mm for silty clay loam through 
heavy clay were used as selected previously in Sec- 
tion I. These classes were supported by R. De Jong 
(personal communication) who summarized the mea- 
sured data from over 300 Saskatchewan soil profiles 
recorded in CanSIS. 






15 



The AWC map of Saskatchewan soils compiled origi- 
nally at a scale of 1:1 million was generalized and 
shown at a scale of 1:2 million (Section I, Figure 1). 

2.2 CLIMATIC DATA 

Daily maximum and minimum temperatures and 
daily precipitation as reported in monthly record of 
the Atmospheric Environment Services were used in 
the calculation of water deficits for wheat from plant- 
ing to the soft dough stage. Daily temperatures were 
used to derive potential evapotranspiration (Baier 
and Robertson 1965). The same stations were used as 
reported previously in Section I of this report. 

2.3 WATER DEFICIT ESTIMATION PRO- 
CEDURES AND MAP COMPILATION 

Water deficits to the soft dough stage are calculated 
according to the following procedures. Soil moisture 
reserves for planting spring wheat for the individual 
years are based on the Versatile Soil Moisture 
Budget developed by Baier and Robertson (1966) and 
obtained using the soil moisture estimator program 
described by Baier et al. (1972). A complete listing of 
the computer program used to obtain soil moisture 
estimates for the accompanying map can be obtained 
from the Agrometeorology Section of the Land Re- 
source Research Institute, Agriculture Canada (Pro- 
gram File No. B234). 

Calculations started with soil moisture reserves at 
May 1 planting. If moisture reserves are below 50% 
of AWC, the amount by which they are less than 50% 
AWC is the water deficit at planting. If plant avail- 
able water is F50% AWC, the water deficit at plant- 
ing is zero. From planting to emergence (10 days) 
water is removed at 75% potential evapotranspira- 
tion (PE) and from emergence to soft dough at 100% 
PE. Water is added according to the rainfall. When 
plant available water drops below 50% AWC at the 
end of the day, the amount of the shortfall is added 
to the water deficit and plant available water is set 
at 50% AWC. Thereby, the crop transpires at the rate 
of PE since plant available water is always at or 
greater than 1/2 AWC (Pair et al. 1969). If rainfall is 
more than enough to fill the soil to capacity, plant 
available water is set at AWC and the excess water 
is considered lost to runoff or deep percolation. This 
procedure is continued to the soft dough stage (89 
days) for each year. These water deficits are averaged 
for all years used during the period of record and then 
recorded on a map. 



The climatic water deficit maps were prepared by 
spatial interpretation of point information as re- 
ported previously in Section I. The map showing 
climatic water deficit isolines for wheat grown to the 
soft dough stage on soils with an AWC of 150 mm is 
presented in Figure 1. Water deficit maps for soils 
with AWC of 100, 200 and 250 mm are similar to 
those compiled by Sly (in press). These water deficit 
maps for wheat were adjusted photomechanically to 
a scale of 1:1 million and produced on matte surface 
film. 

2.4 MAPPING ARIDITY INDEX CLASSES 

A single map showing aridity indices for wheat 
grown to the soft dough stage on soils of different 
AWC was compiled (Figure 2) using water deficit 
maps and plant available water holding capacity 
map as reported previously In Section I of this report. 

3. RESULTS AND DISCUSSION 

Isoline patterns showing long term seasonal water 
deficits for spring wheat grown on soils with 150 mm 
AWC (Figure 1) strongly resembled those reported 
previously for perennials (Section I, Figure 2). How- 
ever, the isoline values for spring wheat were much 
lower than for perennials reflecting fundamental dif- 
ferences in the models used to derive them. For 
wheat, the value is indicative of an accumulated defi- 
cit equivalent to the amount of water required to 
maintain plant available water at 1/2 AWC during a 
growing season of 89 days. In contrast, when water 
available to perennials dropped below 1/2 AWC, a 
standard amount of water equal to 1/2 AWC was 
added. The growing season for perennials was also 
considerably longer extending into the autumn when 
mean daily temperatured dropped below 5.5°C. For 
example, isolines occurring in the extreme south- 
west part of the map area had values of 500 for peren- 
nials compared to 300 for wheat. 

Aridity indices for wheat to the soft dough stage 
ranged from only 50 mm in the subhumid northeast 
to 300 mm in the extreme semi-arid southwest (Fig- 
ure 2). The influence of climate on the aridity index 
is most evident along transect AB where the index for 
soils with 150 mm AWC decreases from 250 mm near 
A to 100 mm near B. This decrease corresponds in 
general to soil zonal patterns as one passes from the 
Brown through the Dark Brown to the Black Soils 
Zone. 



16 




CO 

3 

CO 



I 
"a 
<s 

% 



c 

o 



3 
o 



CO 

aj 
j5 
is 



17 




18 



Aridity indices for wheat are also influenced by the 
available water capacity of different soil areas. As ex- 
pected, this influence is most pronounced in semi- 
arid areas. This is well illustrated within the Dark 
Brown Soil Zone along the short transect C-D (Figure 
2). Clay soils with an AWC of 250 mm are character- 
ized by an AI of 150. In contrast, sandy loam soils 
with an AWC of only 100 mm have an AI of 250; loam 
soils are intermediate. Generally, adjacent soil areas 
with a different AWC have a different AI. However, 
due to the overlay procedures used in merging the 
AWC and climatic water deficit maps there are cases 
where adjacent areas of differing AWC have the 
same AI. These nearly always occur near the location 
of isolines on the climatic water deficit maps. 

In subhumid areas, the influence of AWC on AI was 

less obvious. While the index for sandy soil areas 
with 100 mm AWC was always higher than adjacent 
areas, the same was not true for other capacities par- 
ticularly in the eastern part of the province. This is 
illustrated along transect E-F where soil areas with 
250 mm AWC had the same AI as those with 
capacities of 150 mm. 



4. APPLICATIONS 

A single map showing Aridity Indices of wheat grown 
to the soft dough stage conveniently facilitates com- 
parison among different soil geographic areas. Long 
time average values of aridity indices also provide a 
good standard to which the integrated effects of soil 
and weather on the soil moisture regime in any one 
year can be compared. Obviously, seasonal index 
values which increase markedly above the long term 
averages provide an objective numerical indication 
of drought possibilities. 

It should be pointed out that this aridity index is 
cumulative over the growing season and will not be 
reduced even if much more favorable growing wea- 
ther develops during the later growing stages. Under 
these conditions, the exceptional recuperative pow- 
ers of the wheat plant will not necessarily be re- 
flected in the final index value. Additional work 
must be done to determine more adequately the rela- 
tion between the aridity index at various develop- 
mental stages of the wheat crop and its final yield. 



REFERENCES 

Baier, W., Chaput, D.Z., Russelo, DA., Sharp, W.R. 1972. Soil moisture estimator program system. Tech. 
Bull. 78. Agrometeorol. Sect. Res. Branch, Agric. Can. 55 p. 

Baier, W. and G. W. Robertson. 1966. A new versatile soil moisture budget. Can. J. Plant Sci. 46: 299-315. 

Baier, W. and G.W. Robertson. 1965. Estimation of latent evaporation from simple weather observations. 
Can. J. Plant Sci. 45: 276-284. 

De Jong, E. 1967. Moisture Retention of Selected Saskatchewan Soils In Soil Plant Nutrient Research Re- 
port. Saskatchewan Institute of Pedology Report No. M6. Univ. of Saskatchewan, Saskatoon. 

De Jong, R. and K. Loebel. 1982. Empirical relations between soil components and water retention at 1/3 
and 15 atmospheres. Can. J. Soil Sci. 62: 343-350. 

Pair, C.H., Hinz, W.W., Reid, W. and Frost, K.R. 1969. Sprinkler Irrigation. Sprinkler Irrigation Assn., 
Washington, D.C. 444 p. 

Sly, W.K. 1984. Water deficit maps for spring wheat. In Agroclimatic Atlas of Canada. Derived Data. Ag- 
rometeorology Section, L.R.R.I., Res. Branch, Ottawa, Canada. 

Verma, I.R 1968. Moisture Balance in Soils of the Edmonton Area. Ph.D. Thesis Dept. Soil Sci. Univ. of 
Alberta. 204 p. 



LIBRARY / BIBLIOTHEQUE 



AGRICULTURE CANADA OTTAWA K1A 0C5 

3 T073 00031305 A